In a prior-art reference, EP 0 705 445 A1, an apparatus for measuring the dimensions of an object is disclosed. The apparatus includes means for directing a light beam towards the object, means for registering the light beams that are reflected from the object, and means for causing the light beam to sweep across the object, wherein the sweep of the light beam defines a plane that is perpendicular to a fixed reference plane. A polygonal mirror unit receives laser light and reflects it in a fan-shaped form toward a stationary angled mirror unit, which directs the light towards a double-curved stationary mirror unit which reflects the beam onto the object. The individual mirrors of the polygonal unit are adjustable. The apparatus further comprises means for relative movement between the apparatus and the object which is to be measured and means for calculating the time it takes for the light beams to travel to and from the object.
A major problem that arises in such applications is the so-called shadowing effect, where some parts on the object surface block the view of other parts on the object from the sensor's field of view, for example if the objects under inspection have an irregular shape and/or an uneven surface.
WO 94/15173 A1 discloses a sensing device for three-dimensional surface scanning based on the concept of a scanning sensor which projects two stripes of laser light and views these two stripes from two viewpoints using the viewing means. There is relative movement between the scanning sensor and the object being scanned. The scanning sensor operates on the principle of structured light triangulation. By using this method acquisition of 3D-information or distance-information of an object is based on a view from at least two different angles. The sources of structured light are usually two lasers at an angle towards each other, but may also be one laser and an optical arrangement of mirrors and beam splitters. The concept of two viewpoints may be realized by means of two CCD matrix arrays or by one CCD matrix array and four mirrors.
The apparatus described in WO 94/15173 A1 has the disadvantage of being very complex, particularly if it is to be implemented with only one laser as sending device and one CCD matrix array as receiving device, because that kind of reduction of core optical devices of a device operating on the principle of structured light triangulation would require on the one hand a laser imaging system with a beam splitter and on the other hand a further arrangement of four mirrors.
The problem to be solved by the invention is to obtain multiple views of an object by means of one opto-electronic sensor with considerably lower complexity and as a consequence lower costs compared to devices known in prior art.